System and method of supporting packet-switched handover

ABSTRACT

A system and method of supporting packet-switched handover of a mobile station (MS) from a GERAN/UTRAN cell to a Generic Access Network (GAN) cell within a GAN. If the MS is within coverage of the GAN cell, the MS registers within the GAN triggering initiation of the packet-switched handover from the GERAN/UTRAN cell to the GAN cell. A preparation phase is then conducted for executing the packet-switched handover. The preparation phase includes identifying the MS context as part of the preparation phase and activating the GA-PSR TC towards the MS. Next, the packet-switched handover is executed, resulting in the MS switching to GAN mode. The MS then begins transferring packets via the GAN cell. The system and method also supports a packet-switched handover from the GAN cell to the GERAN/UTRAN cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/804,613, filed Jun. 13, 2006, the disclosure of which is herebyincorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

NOT APPLICABLE

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISC APPENDIX

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BACKGROUND OF THE INVENTION

This invention relates to communication systems. More particularly, andnot by way of limitation, the invention is directed to a system andmethod of supporting packet-switched handover.

Provisions for packet-switched (PS) handover are included in 3^(rd)Generation Partnership Project (3GPP)/GERAN specifications. Theseprovisions allow for PS handover between GPRS/EDGE radio access network(GERAN) and UMTS terrestrial radio access network (UTRAN) cells. PShandover principles are defined in 3GPP TS 43.129 in 3GPP Release-6.

A 3GPP work item, “Evolved UTRA and UTRAN” (E-UTRA and E-UTRANrespectively), defines Long-Term Evolution (LTE), designed to improveefficiency, lower costs and improve services for 3GPP-based accesstechnology. LTE will use Orthogonal Frequency-Division Multiplexing(OFDM) radio technology in the downlink and Single Carrier FrequencyDivision Multiple Access (SC-FDMA) for the uplink, allowing at least 100Mbps peak data rate for downlink data rate and 50 Mbps for uplink datarate. LTE radio can operate in different frequency bands and istherefore very flexible for deployment in different regions of theworld, where different frequency bands might be licensed.

In addition to the Radio Access Network (RAN) standardization, a 3GPPSystem Architecture Evolution (SAE) work item is being worked on todevelop an evolved core network (CN) for LTE networks. The SAE corenetwork is made up of core nodes, which may be further split intoControl Plane (Mobility Management Entity, MME) nodes and User PlaneGateway (Serving Gateway and Packet Data Network (PDN) Gateway) nodes.In this application, the term Access Gateway (AGW) is used to depictboth the Serving Gateway and the PDN Gateway nodes and functions. In theterminology currently used, AGW contains both User Plane Entity (UPE)and Inter-Access Anchor (IASA) functionality. The MME is connected to anE-UTRAN NodeB (eNodeB) via a S1-MME interface, and the AGW (i.e. theServing Gateway) is connected to an eNodeB via an S1-U interface.

Currently, PS handover procedures allow for minimal serviceinterruptions at network-controlled cell change by utilizing theprinciple of make-before-break meaning that the radio resources in thetarget cell are allocated before the mobile station (MS) moves to thetarget cell. In addition, the Location Area Updating (LAU) and RoutingArea Updating (RAU) procedures as defined in 3GPP TS 24.008 areperformed in parallel with the flow of user plane PS data during the PShandover execution phase to help minimize the interruption to user planePS data flow experienced during PS handover.

However, currently there are no provisions for PS handover between aGERAN/UTRAN and a Generic Access Network (GAN) cell, between a GERAN andan Enhanced-UTRAN (i.e., LTE) cell, or between a LTE and a GAN cell.Specifically, there are no systems or methods for allowing PS handoverbetween GERAN and GAN cells or between UTRAN and GAN cells or betweenLTE and GAN cells. Generic Access to the A and Gb interfaces is definedin 3GPP TSs 43.318 and 44.318. Vocabulary for 3GPP specifications isalso defined in 3GPP TS 21.905 and is also utilized in the followingdescription.

Without the capability of a PS handover procedure during a cell changeto or from a GAN cell, service interruptions are increased and aredetermined by the time required to first complete the LAU and RAUprocedures in the new cell (or relevant other similar procedures for LTEand SAE, for example Tracking Area Updates (TAU)) as well as by the timerequired to establish the necessary radio resources in the new cell. Inthe case where the MS also changes SGSN when performing cell change toor from a GAN cell, performing the RAU procedure means that the relevantinformation for the MS is retrieved from the previous (source) SGSN andforwarded to the new current (i.e., target) SGSN, which furtherincreases the service interruption time. In addition, radio resourceestablishment time is an issue when a mobile station (MS) moves into aGERAN cell, given the nature of temporary block flow (TBF) establishmentprocedures.

Additionally, without a PS handover procedure for use during cell changeto and from GAN cells, TBFs in a GERAN cell (and Radio Access Bearers(RABs) in a UTRAN cell) would need to be dropped prior to GAN rove-in(where rove-in implies a cell change procedure performed without usingthe PS handover procedure). The equivalent GAN radio resource, GenericAccess-Packet-Switched Resources (GA-PSR) Transport Channel (GA-PSR TC),would then also need to be established after the rove-in, both of which(i.e. dropping of radio resources in the GERAN/UTRAN and allocatingradio resources in the GAN cell) would add to the service interruptionexperienced by active PS services. If voice over IP (VoIP) is supportedon one of the TBFs/RABs prior to cell change, then releasing the TBF/RABprior to rove-in forces Session Initiated Protocol (SIP) signaling to beonce again invoked in order to set up the VoIP session after rove-in tothe new cell, thereby causing a corresponding delay.

A system and method of supporting PS handover between a GERAN or UTRANcell or LTE cell and a GAN cell is needed to allow packet data transferto occur while LAU and RAU procedures are ongoing and to avoid incurringdelays in performing SIP signaling after cell change. This isparticularly important since GERAN specifications are moving towardfully supporting VoIP service (e.g., with the specification of reducedtransmission times and fast acknowledgement/no acknowledgement reportingas part of the Latency Reduction work effort) which makes avoidance ofadditional SIP signaling in the new cell (i.e. prior to PS serviceresumption) even more important.

Thus, it would be advantageous to have a system and method of supportingPS handover between GERAN or UTRAN cells and GAN cells. The presentinvention provides such a system and method.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to a method ofsupporting packet-switched handover of a mobile station (MS) from afirst cell compatible and located within a first network to a GenericAccess Network (GAN) cell compatible and located within a GAN. Themethod begins by an MS determining if it is within coverage of the GANcell. Next, the MS registers within the GAN while maintaining fullconnectivity with the first cell and then triggers an initiation of thepacket-switched handover from the first cell to the GAN cell. Apreparation phase, which includes the allocation of a GA-PSR TC in theGAN cell, is then conducted prior to executing the packet-switchedhandover. The PS handover is then executed, and as a result, the MS isthen switched to the GAN mode. The MS may then transfer packets via theGAN cell.

In another aspect, the present invention is a system for supportingpacket-switched handover of an MS. The system includes a first cellcompatible with a first network and the MS operating within the firstnetwork. The system also includes a GAN cell within a GAN. The systemdetermines if the MS is within coverage of the GAN cell and registersthe MS within the GAN. A trigger is then sent by the MS to initiate apreparation phase for executing the packet-switched handover, therebyactivating a GA-PSR TC during the preparation phase. The PS handover isthen executed, and as a result, the MS is then switched to a GAN mode.The MS then, upon completion of the preparation phase and switching toGAN mode, begins packet transfer via the GAN cell.

In another aspect, the present invention describes a target noderequired for supporting packet-switched handover of a MS from a firstcell compatible and located within a first network to a GAN cellcompatible and located within a GAN. The target node registers the MS(the registration can be MS initiated or network initiated) within theGAN when the MS is within a coverage area of the GAN cell. The targetnode also receives a handover request from an SGSN as part of thehandover preparation phase, identifies the MS associated with thehandover request, activates the GA-PSR TC during the preparation phasetowards the identified MS and, upon completion of the preparation phase,returns the handover command (as part of the handover requestacknowledgement) to the MS via the SGSN that sent the handover request.The target node is a network controller operating within the GAN andsupports the handover from the first cell to the GAN cell.

In still another aspect, the present invention is a method of supportingpacket-switched handover of an MS from a GAN cell compatible and locatedwithin a GAN to a second cell compatible and located within a secondnetwork. The method begins by determining that the quality of thecurrent GAN cell is deteriorating and that the MS is within coverage ofthe second cell. This determination may take place locally in the MSand/or be assisted by the GAN network. Next, the MS triggers aninitiation of the packet-switched handover from the GAN cell to thesecond cell via the Generic Access Network Controller (GANC). Apreparation phase is then conducted prior to executing thepacket-switched handover to ensure packet radio resources are availableand reserved for the MS in the second cell. The MS is then switched to amode compatible with the second cell. The MS may then transfer packetsvia the second cell using the packet radio resources reserved during thepreparation phase.

In another aspect, the present invention is a system for supportingpacket-switched handover of a MS. The system includes a GAN cellcompatible and located within a GAN network and the MS operating withinthe GAN network. The system also includes a second cell compatible andlocated within a second network. The system determines that the qualityof the current GAN cell is deteriorating and that the MS is withincoverage of the second cell. A trigger is sent by the MS to initiate thepacket-switched handover from the GAN cell to the second cell. Apreparation phase is then conducted prior to executing thepacket-switched handover to ensure packet radio resources are availableand reserved for the MS in the second cell. The MS is then switched to amode compatible with the second network. The MS then transfers packetsvia the second cell using the packet radio resources reserved during thepreparation phase.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

In the following, the features of the invention will be described indetail by showing preferred embodiments, with reference to the attachedfigures in which:

FIG. 1 is a simplified block diagram of a telecommunications system inthe preferred embodiment of the present invention;

FIG. 2 is a signaling diagram illustrating a PS handover procedure froma GERAN cell to a GAN cell according to the teachings of the presentinvention;

FIGS. 3A and 3B are flow charts illustrating the steps of a PS HOprocedure from either a GERAN or an UTRAN cell according to theteachings of the present invention; and

FIGS. 4A and 4B are flow charts illustrating the steps of supporting aPS handover from a GAN cell to either a GERAN or an UTRAN cell accordingto the teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a system and method of supporting PS handoverbetween a GERAN or a UTRAN cell and a GAN cell. FIG. 1 is a simplifiedblock diagram of a telecommunications system 10 in the preferredembodiment of the present invention. Existing mobile networks logicallydivide the infrastructure into a Core Network and an Access Network. Thebasic Core Network includes circuit-switched nodes, such as MobileSwitching Centers (MSCs), packet-switched nodes, such as General PacketRadio Service support nodes (SGSNs) and other control and/or databasenodes, such as Home Location Registers (HLRs). The basic Access Networkincludes radio control nodes and radio access nodes. The radio controlnodes may include Base Station Controllers (BSCs) for GSM (Global Systemfor Mobile Communications) radio networks and Radio Network Controllers(RNCs) for UMTS (Universal Mobile Telecommunications System) radionetworks. In addition, the radio access nodes may be Base TransceiverStations (BTSs) for GSM radio networks and Node Bs for UMTS radionetworks. The combination of BSCs and BTSs is called Base StationSubsystem (BSS) for GSM networks and the combination of RNCs and Node Bsis called Radio Network Subsystem (RNS) for UMTS networks. Referring toFIG. 1, the telecommunications system includes a mobile station 12operating in the telecommunications system 10. The system includes a BSS16 and a GERAN cell 18 within a GERAN 20. The network also includes aUTRAN cell 22 and a RNS 24 within a UTRAN 26. A GAN cell 28 and aGeneric Access Network Controller (GANC) 30 operate within a GAN 32. Inaddition, the telecommunication system includes a SGSN 40. Forsimplicity, only components relevant to the PS handover procedure arediscussed, but it should be understood that the telecommunication systemmay utilize other components.

In a first embodiment, a PS handover is conducted from either the GERANcell 18 or the UTRAN cell 22 to the GAN cell 28. The mobile station isactive in conducting one or more packet data sessions in either theGERAN cell or the UTRAN cell. The MS utilizes neighbor cell listinformation for measurement reporting purposes prior to the MS detectingentry into a GAN coverage area of the GAN cell 28. Next, the MS detectsthe presence of GAN coverage and performs a GAN registration procedure.The MS 12 then receives the Absolute Radio Frequency Channel Number(ARFCN) and the Base transceiver station Identity Code (BSIC) of thecorresponding GANC 30 as defined in 3GPP TS 43.318 and 44.318. As partof the GAN registration process, the GANC 30 stores an MS context foreach MS that is successfully registered. The MS context containsinformation reported by the MS during GAN Registration, such as the MSIP address and the MS Transmission Control Protocol (TCP) connectionidentifier (socket). In addition, the International Mobile SubscriberIdentity (IMSI) is used as the main identifier to find a correct MScontext.

If the ARFCN of the GANC 30 for which GAN registration was successfullyperformed is included in the neighbor cell list of the current GERANcell 18 or the UTRAN cell 22, the MS 12 begins sending measurements forthe ARFCN corresponding to the GAN cell 28. The MS 12 may then report anRXLev of 63 as defined in 3GPP TS 43.318 and 44.318.

By sending measurements that include the ARFCN corresponding to the GANcell, it may be considered as implicitly indicating that the MS supportsPS handover to a GAN cell 28. Thus, it may not be necessary to modifythe MS Radio Access Capability (RAC) IE to explicitly indicate MSsupport for PS handover from a GERAN cell 18 to a GAN cell 28.Transmission of the measurements that include the ARFCN corresponding tothe GAN cell 28 may also indicate that the MS 12 desires a PS handoverto the corresponding GAN cell 28.

If the BSS 16 or the RNS 24 knows that a specific ARFCN corresponds to aGAN cell, the MS may then send the network a measurement report thatindicates an RXLev of 63 for that ARFCN implicitly indicating itsupports PS handover to a GAN cell 28 (i.e. an MS that supports PSHandover to GAN can explicitly avoid indicating an RxLev of 63 for allmeasurement reports except those corresponding to a GAN cell). Since inthis case the BSS/RNS knows that the reported ARFCN corresponds to a GANcell, it will then know that PS Handover can be used to accomplish cellchange instead of legacy methods such as sending the MS a Packet CellChange Order. If the BSS 16/RNS 24 does not know that a specific ARFCNcorresponds to a GAN cell, the MS sending a measurement report to thenetwork that indicates that an RXLev of 63 for that ARFCN is stillsufficient to implicitly indicate that the MS supports PS handover toGAN. This can be accomplished because an MS that supports PS handover toa GAN cell may be required to only send the network a measurement reportthat indicates an RXLev of 63 for an ARFCN that it has determined to beassociated with GAN service (i.e. the MS never indicates an RXLev of 63for non-GAN neighbor cells). In this case, a BSS/RNS that supports PSHandover to GAN will therefore view the reporting MS as either a non-GANPS Handover capable MS indicating an RxLev of 63 for a GERAN neighborcell or a GAN PS Handover capable MS indicating an RxLev of 63 for a GANneighbor cell. However, if there is a lack of available systeminformation for the reported neighbor cell, the BSS/RNS mayconclude/deduce that it is a GAN neighbor cell (i.e., the BSS/RNS neverneeds to send the MS system information corresponding to a GAN neighborcell 28, since the MS acquires the corresponding system informationduring GAN registration). As such, once the BSS/RNS hasconcluded/deduced that the reported ARFCN corresponds to a GAN cell, theBSS/RNS then knows that PS Handover can be used to accomplish cellchange instead of legacy methods, such as sending the MS a Packet CellChange Order.

Alternatively, rather than sending a measurement report to trigger PSHandover to the GAN cell, a new PACCH message may be sent from the MS 12to the BSS 16 or a new Radio Resource Control (RRC) message may be sentfrom the MS 12 to the RNS 24 where both messages would include the ARFCNcorresponding to the GAN cell. PS handover from the GERAN cell 18 or theUTRAN cell 22 to the GAN cell 28 therefore requires that the MS be in apacket transfer mode (while in a GERAN cell) or be in RRC Connected mode(while in a UTRAN cell) to provide the BSS 16/RNS 24 with a PACCH/RadioResource Control (RRC) message based indication that it supports PShandover to a GAN cell 28.

Assuming neighbor list (NL) information in the GERAN cell 18 or UTRANcell 22 does not indicate the presence of a GAN cell 28, but that the MShas discovered an acceptable GAN cell 28 while performing GANregistration, (which indicates a secure tunnel has been established inthe GAN cell and authentication has been performed as necessary), the MSmay indicate a desire for PS handover to the GAN cell 28 by sending theBSS 16 a newly defined Packet Associated Control Channel (PACCH) message(e.g., a GAN-SERVICE-AVAILABLE message) or a similar RRC message to theRNS 24 on the uplink DCCH. The PACCH message may provide informationabout the SGSN 40 associated with the GAN cell 28 (e.g., in the form ofa Routing Area Identifier), target cell ID, ARFCN corresponding to theGAN cell, etc. so that the PS handover preparation phase can be directedto the intended SGSN 40 and the intended GAN cell 28.

The transmission of such a new PACCH message while the MS is in packettransfer mode may implicitly indicate that the MS is capable of PShandover to the GAN cell and that the MS desires to receive a PShandover to the corresponding GAN cell 28. Similarly, in a situationwhere the MS is actively sending packet data in a UTRAN cell in RRCConnected mode, it is not necessary to modify the UEmulti-mode/multi-RAT (Radio Access Technology) capability InformationElement (IE) to explicitly indicate MS support for PS handover from aUTRAN cell to a GAN cell. Instead, the MS sends the RNS a new RRCmessage (indicating it is capable of PS handover) while it has one ormore RABs supporting PS domain services in RRC Connected mode.

A BSS (or RNS) that supports PS Handover to a GAN cell may then initiatethe PS handover preparation phase essentially in accordance with thetypical legacy PS handover preparation process for the intra-RAT case(GERAN to GERAN) or the inter-RAT case (UTRAN to GERAN). One exceptionis that the GANC 30 performs a GA-PSR TC activation during the PShandover preparation phase (i.e., while the MS is still in GERAN/UTRANmode). The GANC 30 sends the MS a GA-PSR-ACTIVATE-UTC-REQ message andreceives a GA-PSR-ACTIVATE-UTC-ACK message from the MS during the PShandover preparation phase to prepare the GA-PSR Transport Channel. Thisis triggered when the GANC receives the PS HANDOVER REQUEST message fromthe SGSN. As the IMSI is always included in this message, the GANC canidentify the MS context (established during GAN registration), the MS IPaddress, and the TCP connection that relates to the PS Handoverpreparation phase request and so trigger the GA-PSR TC activationtowards the correct MS using that TCP connection. In addition, it ispossible that the MS holds two separate radio interfaces and is able tocommunicate with GERAN or UTRAN and GAN networks simultaneously usingthese radio interfaces.

Another alternative for the GA-PSR TC activation during the PS handoverpreparation phase may be utilized and applied when a new PACCH/RRCmessage is used to trigger the PS HANDOVER from the GERAN cell 18/UTRANcell 22 to the GAN cell 28. Specifically, the MS 12 may register withthe GANC 30 prior to sending the new PACCH message (on the GERAN radiointerface) or new RRC message (on the UTRAN radio interface) to indicatethe preference to trigger PS handover to the corresponding GAN cell. TheMS may then reserve the local side of the GA-PSR TC (i.e. an UDP-port tobe used) and includes the reserved identifier (e.g. UDP-port) in the newPACCH message/RRC message that it sends to the BSS/RNS. The BSS 16/RNS24 then triggers the PS handover preparation phase essentially inaccordance with the existing legacy PS handover preparation phase withone exception. The identifier which is locally reserved by the MS andreceived by the BSS/RNS in the new PACCH message/RRC message (e.g.UDP-port) is also included in the Base Station Subsystem GPRS Protocol(BSSGP) PS HANDOVER REQUIRED message/Radio Access Network ApplicationPart (RANAP) Relocation Required message which the BSS/RNS sends totrigger the PS handover preparation phase while the MS is in thecoverage area of a GERAN/UTRAN cell. This message is sent from thesource BSS 16/RNS 24 to the SGSN handling the GANC 30. The GANC 30 thenreceives the PS HANDOVER REQUEST message and, as the IMSI is alwaysincluded in this message, the GANG can then identify the MS context(established during GAN registration) and MS IP address that relates tothe PS Handover preparation phase request. The locally reservedidentifier initially received by the source BSS 16/RNS 24 in the newPACCH message/RRC message (e.g. UDP-port) is also received by the GANC30 in the PS HANDOVER REQUEST message. At this stage, the GANC is awareof both the IP address (retrieved from the MS context) and the UDP port(received in the PS HANDOVER REQUEST message) to be used for the GA-PSRTC.

In this alternate embodiment, rather than performing the GA-PSR TCactivation towards the MS as discussed above, in this next step, theGANC also reserves the local identifiers for the GA-PSR TC which aresent to the MS by including them in the GAN PS HO COMMAND message thatis returned to the MS during the PS handover preparation phase. The GANCincludes the GAN PS HO COMMAND message in the PS HANDOVER REQUESTACKNOWLEDGE message, which is then forwarded to the MS using existingpreparation phase procedures. The GAN PS HO COMMAND may be a standard PSHandover Command message as defined in 3GPP TS 44.060 v6.21.0.

Once the MS receives the GAN PS HO COMMAND message via the radiointerface of the GERAN cell 18 or UTRAN cell 22, the MS has all therequired information for the GA-PSR TC and may start sending data in theGAN cell. As such, the GA-PSR TC activation procedure normally performedvia the radio interface of the GAN cell 28 may not be explicitlyperformed, but rather implicitly performed using the PS handoverpreparation phase and execution phase procedures when a locally reservedidentifier is received by the source BSS 16/RNS 24 in the new PACCH/RRCmessage (e.g. UDP-port) followed later by the MS receiving the localidentifier reserved by the GANC in the GAN PS HO COMMAND message.

The PS handover between GERAN or UTRAN cells and GAN cells is consideredas primarily either an intra-RAT PS HO (GERAN to/from GERAN) or aninter-RAT PS HO (UTRAN to/from GERAN) as will be shown by thecorresponding stage 2 scenarios when they become available (i.e. theywill show that there are differences from PS handover between two GERANcells).

After completion of the PS handover preparation phase, the PS handoverexecution phase begins by a PS Handover command being sent to the MS 12in the GERAN cell 18 or the UTRAN cell 22. The handover command sent tothe MS in the GERAN/UTRAN cell does not actually contain a tunneled PSHandover command providing the MS with information unique to GAN mode(except for the case of an implicit GA-PSR TC activation procedure asdescribed above where the PS Handover command would include GAN modespecific information sent to the source BSS (or source RNS) during thePS handover preparation phase). Rather, upon receiving the PS Handovercommand the MS 12 typically only needs to treat it as an indication thatit is to switch to GAN mode and begin using the already activated GA-PSRtransport channel. In addition, the MS does not need to acquire systeminformation for the target GAN cell 28 prior to accepting a PS handovercommand to that cell since the necessary system information has alreadybeen obtained by the MS during the GAN registration procedure.

The GANC 30 may use a variety of methods to determine that the PShandover to GAN was successful so that the PS handover execution phasecan be completed (i.e. so that the source BSS/RNS can be informed thatlocal PS resources can be released). In one embodiment, a new GA-PSRsignaling message such as a “GA-PSR-HANDOVER-COMPLETE” message sent bythe MS to inform the GANC of this success condition may be used. Inanother embodiment, the GANC receives data on the GA-PSR TC establishedduring the particular PS handover for a particular MS.

FIG. 2 is a signaling diagram illustrating a PS handover procedure froma GERAN cell to a GAN cell according to the teachings of the presentinvention. First, the MS transfers packets at 100 in a GERAN cell 18.Next, GAN registration signaling 102 occurs between the GANC 30 and theMS 12. The MS 12 then provides a triggering mechanism to the BSS 16 in104. The trigger mechanism may be any trigger which informs the BSS 16that the MS 12 is ready for a handover to a GAN cell 28 as discussedabove. Next, in 106, the BSS 16 initiates the PS handover preparationphase by communicating with the SGSN 40. In 108, the SGSN 40 sends a PShandover request to the GANC 30 in accordance with the typical legacy PShandover preparation process for the intra-RAT case (GERAN to GERAN) orthe inter-RAT case (UTRAN to GERAN). One exception to typical legacyprocedures is that the GANC 30 performs a Generic Access-Packet-switchedResources (GA-PSR) Transport Channel (GA-PSR TC) activation during thePS handover preparation phase (i.e., while the MS is still inGERAN/UTRAN-mode). The GANC 30 sends the MS a GA-PSR-ACTIVATE-UTC-REQmessage 110. In turn, the MS sends a GA-PSR-ACTIVATE-UTC-ACK message 112to the GANC during the preparation phase to confirm allocation of theGA-PSR Transport Channel. The GANC 30 then sends a PS handover requestacknowledgement 114 to the SGSN 40.

The SGSN 40 then sends a PS handover required acknowledgement message116 to the BSS 16. The PS handover is then executed by the BSS 16sending a PS handover command message 118 to the MS 12. The MS thensends a GA-PSR-HANDOVER-COMPLETE message 120 to the GANC 30 and thenswitches to GAN mode in 122 In 124, uplink and downlink data is sent andreceived via the GAN cell 28 in parallel with RAU and LAU. It should beunderstood that the same signaling diagram may be utilized for a PShandover procedure from a UTRAN cell to a GAN cell.

FIGS. 3A and 3B are flow charts illustrating the steps of a PS HOprocedure from the GERAN or UTRAN cell according to the teachings of thepresent invention. With reference to FIGS. 1-3, the method will now beexplained. The method may be utilized for either a GERAN cell or a UTRANcell. The method begins in step 200 where the MS 12 transfers packets inthe GERAN cell 18 or the UTRAN cell 22. Next, in step 202, it isdetermined if the MS detects that it is within coverage of the GAN cell28. If it is determined that the MS is not within the coverage area ofthe GAN cell, the method moves to step 200 where the MS 12 continues totransfer packets in the GERAN/UTRAN cell.

However, if it is determined that the MS is within the coverage area ofthe GAN cell 28, the method moves from step 202 to step 204 where a GANregistration procedure is conducted between the GANC 30 and the MS 12.In step 206, the MS sends a PS handover triggering mechanism to the BSS16 or RNS 24. The triggering mechanism may be any mechanism to indicatethat the MS supports and requests PS handover to a GAN cell. Thetriggering mechanism may be the transmission of measurements for theARFCN corresponding to the GAN cell and reporting an RXLEV of 63. Bysending measurements which include the ARFCN corresponding to the GANcell combined with the BSS/RNS ability to detect the nature of thereported cell as described above, the MS is implicitly indicating thatthe MS supports PS handover to a GAN cell. An alternative triggermechanism to sending measurements (to trigger BSS/RNS recognition of MSsupport for PS handover) is to send a new PACCH message/RRC message fromthe MS to the BSS 16/RNS 24. Upon receipt of the trigger by the BSS16/RNS 24, the BSC/RNS initiates the PS handover preparation phase instep 208. The preparation phase is similar to the legacy PS handoverpreparation phase. One exception is that the GANC 30 performs a GenericAccess-Packet-switched Resources (GA-PSR) Transport Channel (GA-PSR TC)activation during PS handover preparation phase (i.e., while the MS isstill in GERAN/UTRAN-mode). The GANC 30 sends the MS 12 aGA-PSR-ACTIVATE-UTC-REQ message 110. In turn, the MS 12 sends aGA-PSR-ACTIVATE-UTC-ACK message 112 to the GANC during the preparationphase to confirm allocation of the GA-PSR Transport Channel. The GANC 30then sends a PS handover request acknowledgement 114 to the SGSN 40. TheSGSN then sends a PS handover required acknowledgement message 116 tothe BSC (a Relocation Command would be sent from the SGSN to the RNC forthe case of UTRAN to GAN PS Handover).

The method then moves to step 210 where the PS handover is then executedby the BSC/RNC sending a PS handover command message 118 to the MS 12.In step 212, the MS 12 sends a GA-PSR-HANDOVER-COMPLETE message 122 tothe GANC and then switches to the GAN mode. In step 214, uplink anddownlink data is sent and received via the GAN cell 28 in parallel withRAU and LAU.

PS handover from a GAN cell to a GERAN/UTRAN cell is similar to thepreparation and execution phase as for legacy intra-RAT PS handover(GERAN to GERAN) or legacy inter-RAT PS handover (GERAN to UTRAN).However, there are some differences. During GAN registration, the MS 12sends the GANC 30 a GA-RC Register Request message that includes the GANClassmark IE which may be modified to indicate an MS is capable of PShandover from a GAN cell to a GERAN/UTRAN cell. In an alternateembodiment of the present invention, a specific type of GAN measurementinformation is defined for the PS handover procedure (i.e., compared tothe GA-CSR HANDOVER INFORMATION message for CS handover). The GANC 30may then detect that an MS 12 supports GAN PS handover if the MS 12sends these new messages to the GANC.

In addition, at any point when a GA-PSR transport channel is active, theGANC 30 may determine that the MS is better served in a GERAN/UTRAN celland therefore trigger the PS handover procedure if the MS 12 supports PShandover. The GANC may determine this trigger based on measurementinformation sent by the MS 12 to the GANC 30 while in the GA-PSR ACTIVEstate in GAN mode. For example, the GANC 30 may send the MS 12 anexplicit GA-PSR signaling message that indicates when the MS shouldstart sending measurement reports providing information aboutGERAN/UTRAN cells. Alternatively, the MS 12 may perform localmeasurements and based on these send the measurement reports providinginformation about GERAN/UTRAN cells to the GANC 30.

A GA-PSR Handover Command message may be sent to the MS in the GAN cellduring the execution phase and may then clearly distinguish between thecases of PS handover to GERAN cell and a UTRAN cell since the MSrequires a unique way to determine which type of tunneled PS handovercommand is present in the GA-PSR Handover Command message.

In the case when a PS handover is conducted from a GAN cell to a GERANcell, the MS may be provided with target cell system information duringthe PS handover execution phase (e.g., as part of the GA-PSR HandoverCommand). The GANC may be able to acquire this system information usingeither Radio Information Management (RIM)/Network Assisted Cell Change(NACC) procedures or using the target BSS to source BSS transparentcontainer sent by the target BSS during the PS handover preparationphase.

FIGS. 4A and 4B are flow charts illustrating the steps of supporting aPS handover from a GAN cell 28 to either a GERAN cell 18 or an UTRANcell 22 according to the teachings of the present invention. Withreference to FIGS. 1 and 4, the method of the present invention will nowbe explained. The method begins in step 300 where the MS 12 transferspackets in a GAN cell 28. Next, in step 302, it is determined that thequality of the current GAN cell is deteriorating and that the MS detectsthat the MS 12 is within the coverage area of either the GERAN cell orthe UTRAN cell (or both). If it is determined that the MS 12 is notwithin the coverage area of the GERAN/UTRAN cell, the method moves tostep 300 where the MS 12 continues to transfer packets in the GAN cell28 as long as possible.

However, if it is determined that the MS 12 is within the coverage areaof either the GERAN cell or the UTRAN cell and that the quality of thecurrent GAN cell is deteriorating, the method moves from step 302 tostep 306, where the MS 12 sends a triggering mechanism to the GANC 30.The triggering mechanism may be any mechanism to indicate that the MS 12supports PS handover to a GERAN/UTRAN cell. Upon receipt of the triggerby the GANC 30, the GANC initiates the PS handover preparation phase instep 308. The method then moves to step 310 where the PS handover isthen executed by the GANC 30 sending a GAN PS Handover Command messageto the MS 12. The MS 12 is preferably provided with target cell systeminformation during the PS handover execution phase (i.e. at least for PShandover from a GAN cell to a GERAN cell). In step 312, the MS 12switches to GERAN/UTRAN mode. In step 314, uplink and downlink data issent and received via the GERAN/UTRAN cell in parallel with RAU and LAU.

It should be understood, although the present invention describessupport of PS handover between GAN cells and GERAN and UTRAN cells, thepresent invention may also be utilized with other types oftelecommunication systems which encompass other types of radio accessnetworks, such as Advanced Mobile Phone Service (AMPS) system, theNarrowband AMPS system (NAMPS), the Total Access Communication System(TACS), the Personal Digital Cellular (PDC) system, the United StatesDigital Cellular (USDC) system, code division multiple access (CDMA)system or the E-UTRAN system (also know as a Long Term Evolution systemor simply an LTE system).

Although preferred embodiments of the present invention have beenillustrated in the accompanying drawings and described in the foregoingDetailed Description, it is understood that the invention is not limitedto the embodiments disclosed, but is capable of numerous rearrangements,modifications, and substitutions without departing from the scope of theinvention. The specification contemplates all modifications that fallwithin the scope of the invention defined by the following claims.

1. A method of supporting packet-switched handover of a mobile station(MS) from a first cell compatible with a first network to a GenericAccess Network (GAN) cell compatible and located within a GAN, themethod comprising the steps of: determining if the MS is within coverageof the GAN cell; registering the MS within the GAN, wherein theregistering further comprises creating a MS context and identifying theMS context with an International Mobile Subscriber Identifier (IMSI)associated with the MS; triggering initiation of the packet-switchedhandover from the first cell to the GAN cell; conducting a preparationphase for executing the packet-switched handover, wherein the step ofconducting the preparation phase for executing the packet-switchedhandover includes identifying the MS context, based on the IMSIassociated with the MS, that relates to a packet-switched (PS) Handoverpreparation phase request sent by the MS and activating a GenericAccess-Packet-switched Resources (GA-PSR) Transport Channel from the GANcell towards the MS; switching by the MS to a GAN mode; and transferringpackets via the GAN cell.
 2. The method of supporting thepacket-switched handover as recited in claim 1, wherein the first cellis a GPRS/EDGE radio access network (GERAN) cell and the first networkis a GERAN.
 3. The method of supporting the packet-switched handover asrecited in claim 1, wherein the first cell is a Long Term Evolution(LTE) cell and the first network is a LTE network.
 4. The method ofsupporting the packet-switched handover as recited in claim 1, whereinthe step of triggering initiation of the packet-switched handoverincludes sending a Packet Associated Control Channel (PACCH) messagefrom the MS to the first network.
 5. The method of supporting thepacket-switched handover as recited in claim 4, wherein the PacketAssociated Control Channel (PACCH) message includes aGAN-SERVICE-AVAILABLE message indicating the MS is ready forpacket-switched handover to the GAN cell.
 6. The method of supportingthe packet-switched handover as recited in claim 1, wherein the firstcell is a UMTS terrestrial radio access network (UTRAN) cell and thefirst network is a UTRAN.
 7. The method of supporting thepacket-switched handover as recited in claim 1, wherein the step oftriggering initiation of the packet-switched handover includes sending ameasurement report from the first cell to the first network indicatingreceipt of a specific Absolute Radio Frequency Channel Number (ARFCN) ofa GAN cell, thereby indicating support of packet-switched handover tothe GAN cell.
 8. The method of supporting the packet-switched handoveras recited in claim 1, further comprises the step of sending apacket-switched handover command to the MS.
 9. The method of claim 1,wherein a GAN controller activates the Generic Access-Packet-switchedResources (GA-PSR) Transport Channel towards the MS.
 10. The method ofclaim 1, wherein the MS context comprises information reported by the MSduring GAN Registration including a MS Internet Protocol (IP) addressand the MS Transmission Control Protocol (TCP) connection identifier.11. A system for supporting packet-switched handover of a mobile station(MS), the system comprising: a first cell compatible and located withina first network; the MS operating within a coverage of the first cell; aGeneric Access Network (GAN) cell compatible within a GAN; means fordetermining if the MS is within coverage of the GAN cell; means forregistering the MS within the GAN, wherein the registering furthercomprises creating a MS context and identifying the MS context with anInternational Mobile Subscriber Identifier (IMSI) associated with theMS; means for triggering initiation of the packet-switched handover fromthe first cell to the GAN cell; means for conducting a preparation phasefor executing the packet-switched handover, wherein the means forconducting a preparation phase for executing the packet-switchedhandover includes a means for identifying the MS context, based on theIMSI associated with the MS that relates to a packet-switched (PS)Handover preparation phase request sent by the MS and activating aGeneric Access-Packet-switched Resources (GA-PSR) Transport Channel fromthe GAN cell towards the MS; and means for switching by the MS to a GANmode; whereby the MS transfers packets via the GAN cell upon completionof the preparation phase and switching by the MS to a GAN mode.
 12. Thesystem for supporting the packet-switched handover as recited in claim11, wherein the first cell is a GPRS/EDGE radio access network (GERAN)cell and the first network is a GERAN.
 13. The system for supporting thepacket-switched handover as recited in claim 11, wherein the first cellis a Long Term Evolution (LTE) cell and the first network is a LTEnetwork.
 14. The system for supporting the packet-switched handover asrecited in claim 11, wherein the means for triggering initiation of thepacket-switched handover includes sending a Packet Associated ControlChannel (PACCH) message from the MS to the first network.
 15. The systemfor supporting the packet-switched handover as recited in claim 14,wherein the Packet Associated Control Channel (PACCH) message includes aGAN-SERVICE-AVAILABLE message indicating the MS is ready forpacket-switched handover to the GAN cell.
 16. The system for supportingthe packet-switched handover as recited in claim 11, wherein the firstcell is a UMTS terrestrial radio access network (UTRAN) cell and thefirst network is a UTRAN.
 17. The system for supporting thepacket-switched handover as recited in claim 11, wherein the means fortriggering initiation of the packet-switched handover includes sending ameasurement report from the first cell to the first network indicatingreceipt of a specific Absolute Radio Frequency Channel Number (ARFCN) ofa GAN cell, thereby indicating support of packet-switched handover tothe GAN cell.
 18. A node for supporting packet-switched handover of amobile station (MS) from a first cell compatible with a first network toa Generic Access Network (GAN) cell compatible within a GAN, the nodecomprising: means for registering the MS within the GAN when the MS iswithin a coverage area of the GAN cell, further comprising storing a MScontext and identifying the MS context with an International MobileSubscriber Identifier (IMSI) associated with the MS; and means forreceiving a packet-switched (PS) handover preparation request,identifying the MS context, based on the IMSI associated with the MS,for the PS handover preparation request sent by the MS, activating aGeneric Access-Packet-switched Resources Transport Channel (GA-PSR TC)from the node towards the MS during a packet-switched (PS) preparationphase and responding to the PS handover preparation request with a PShandover preparation request acknowledgement; wherein the node is anetwork controller operating within the GAN and supporting the handoverfrom the first cell to the GAN cell.
 19. The node for supporting thepacket-switched handover as recited in claim 18, wherein the node is aGeneric Access Network Controller.
 20. The node for supporting thepacket-switched handover as recited in claim 18, further comprising:means for identifying a MS context that relates to a PS Handoverpreparation phase request; and means for activating a GenericAccess-Packet-switched Resources (GA-PSR) Transport Channel towards theMS.